1. Field of the Invention
This invention relates, generally, to prosthetic devices. More particularly, it relates to a machine for casting a prosthesis for a lower limb while the stump is under load.
2. Description of the Prior Art
Hard sockets for receiving an amputee patient's stump were originally hand carved from wood and lined with leather to soften the contact between the stump and the socket.
In more modern times, however, devices and methods have been developed that enable a prosthetist to fashion a socket that fits each individual patient. In one well known method, the stump is first inserted into a cushioned liner and the liner is wrapped in plaster. The prosthetist then applies manual pressure to conform the plaster and liner to the shape of the stump; the pressure is applied until the plaster sets. The stump is then removed from the plaster impression, and said impression is used to make a positive of the stump. The hard socket is then made from the positive, employing either casting of thermoset material, or vacuum or pressure forming of a thermoplastic sheet.
One drawback of the manual pressure method is that its success depends to a large degree upon the manual dexterity and skill of the prosthetist. Although a highly skilled prosthetist might be able to exert a nearly uniform pressure on all sections of the plaster, a perfectly fashioned impression is a rarity.
A machine that reduces the level of skill required of the prosthetist and which consistently applies a uniform pressure to the plaster includes a cylindrical bladder that ensleeves the patient's stump after plaster has been applied thereto. A uniform pressure is applied to the exterior of the bladder so that it is driven radially inwardly and transmits the uniform pressure to the plaster. Thus, the bladder supplants the hands of the prosthetist and the pressure is applied uniformly to all sections of the plaster. The result is a better fit than usually provided by the manual method described earlier.
However, both the manual and machine-aided methods described above have an important limitation; they work only when the patient is in a sitting or reclining position, i.e., when there is no load on the stump. Thus, the hard socket fits the stump well when the stump is not bearing the patient's weight, but the fit is not so precise when the stump is bearing weight. Moreover, the known device cannot accommodate above-the-knee amputees.
Still another drawback of the known device is that its bladder is opaque. This prevents the prosthetist from seeing how well the plaster is being pressed against the patient's stump. If the bladder were transparent, the prosthetist could observe the pressurizing process, and could note any locations where the bladder failed to provide the needed pressure on the plaster; corrective measures could then be taken.
The known devices are also deficient to the extent that they often cause discomfort to the amputee because they provide insufficient space at the distal end of the hard socket. Empty space at the distal end of the socket is needed because the stump may have jagged bone residue which cannot comfortably support weight.
What is needed, then, is a prosthetic casting machine having the capability of applying a uniform pressure to plaster that overlies a weight-bearing stump. Another need exists for a transparent bladder. A hard socket made by such a machine would fit the patient well even when the stump is bearing the patient's weight, and would provide an empty space at the distal end of the socket.
Such a casting machine is also needed for above-the-knee amputees.
However, in view of the prior art as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in this art how an improved machine having the desired qualities could be built.